The invention relates to a method of manufacturing a semiconductor device whereby a dopant is provided near a surface of a semiconductor body in a deposition step, after which in a diffusion step said dopant is diffused into the semiconductor body in that the semiconductor body is kept at an elevated temperature for a certain period in a furnace while a process gas is passed through the furnace, after which any oxide layer formed on the surface is removed.
The semiconductor body may be provided with regions of a certain conductivity type by means of the method through deposition and diffusion of a dopant of this conductivity type. Dopant atoms are provided near the surface of the semiconductor body in the deposition step, in general in a region less than 0.5 .mu.m removed from the surface, for example, through implantation or a shallow diffusion, for example, from a process gas or from a doped glass layer. In the diffusion step ("drive-in"), the atoms are subsequently brought to a greater depth below the semiconductor body surface through diffusion and activated through a heat treatment for several hours at a temperature above approximately 1100.degree. C. Process gases used may be, for example, argon, oxygen, nitrogen, or a combination of these gases. After the diffusion step, any oxide layer which has formed on the surface during the deposition or diffusion step is removed, for example, to provide a possibility of manufacturing further regions in the region made by the method or for providing the region manufactured with an electrical connection. The method may be used for providing a semiconductor body with regions of a certain conductivity type. These regions may be used, for example, in diodes, transistors and ICs, for example, as pn junctions, resistors, insulation diffusions, contact zones, and channel stoppers.
European Patent 1609 19 discloses a method of the kind mentioned in the opening paragraph whereby boron is implanted into a silicon semiconductor body with an energy of between 20 and 200 keV and a concentration of between 5 and 15.times.10.sup.14 atoms/cm.sup.2. The implanted boron atoms are then diffused into the semiconductor body in the diffusion step at a temperature of between 1150.degree. C. and 1250.degree. C. for 30 to 300 minutes in a process gas containing a small proportion of oxygen.
It is found in practice that a number of problems arise in semiconductor devices manufactured by the known method. When the known method is used for manufacturing a zener diode, it is found that the diode has a breakdown characteristic, i.e. a transition between conduction and non-conduction of current as a function of the voltage across the diode, which is so gradual that the zener voltage is not well defined and the diode is, for example, useless as a switch in an electric circuit. Furthermore, the known method is found to be not very reliable. Thus properties such as electrical resistance and breakdown voltage of semiconductor devices made by the known method may vary strongly.